Spot welders having multiple tips are useful in many applications. For example, a manifacturer may manufacture a part consisting of two pieces of metal which are to be welded in multiple locations to ensure that the pieces remain joined together. A spot welder having single tip must be moved into multiple positions and weld in each of those positions to join the parts together. However, a multiple tip spot welder need not be moved.
Multi-tip spot welders are usually comprised of a housing or holder which holds multiple weld tip plungers. Generally, the housing is able to move in a vertical direction to cause the weld tips connected to exert pressure on the workpice when welding. Furthermore, because sufficient pressure is required to result in a good weld, in many instances, each weld tip plunger is also able to move vertically, within the housing, and is biased toward the workpiece. For some spot welders, such as the EQUATIP Dual Tip Holder disclosed in U.S. Pat. No. 3,558,847, two weld tip plungers, each biased by a compression spring, are operatively connected such that although the plungers are able to move independent of the housing, they are not able to move independent of each other. Other welders, such as those disclosed in U.S. Pat. Nos. 2,097,377, 3,692,970 and 5,079,400, provide mechanisms whereby each weld tip is able to move in the vertical direction independent of each other and independent of the housing.
In some applications, the voltage required for the weld is such that the weld tip may become excessively hot and may even melt or become deformed. To compensate for the heat generated, a coolant is usually provided to the weld tips to extend their useful life. Traditionally, coolant is introduced to the housing and flows from within the housing to provide coolant to all weld tips by flowing around the biasing mechanism of the weld plunger to the weld tip. Because the weld tip plunger is able to move in a vertical direction, a seal must be provided to keep coolant from flowing outside of the weld tip plunger. For example, an O-ring is used around the weld tip plunger (between the weld tip plunger and housing) in the EQUATIP Dual Tip Holder. However, the requirement of such a seal introduces other problems. The seal may deteriorate resulting in the loss of coolant from what was intended to be a closed system. If coolant loss is sustained, damage to the weld tip results as the weld tip is not sufficiently cooled. Thus, it is desirable to provide a coolant system for a multi-tip spot welder which does not utilize a seal between moving metal parts which may potentially deteriorate and which may result in damage to the weld tip.
Provision of coolant to each weld tip plunger from an external source also presents the problem of connecting many hoses to the spot welder as two hoses, one for the delivery of coolant and one for the removal of heated coolant, are required for each weld tip. Thus, it is desirable to limit the number of hoses connected to the welder from an external coolant source and to limit the length of each hose so as to reduce the possibility of losing coolant either at the coolant hose's connection points or from a break in the hose.
In general, the weld tip is comprised of a hollow weld cap at the operative end of the weld tip through which the coolant flows. U.S. Pat. No. 4,788,407 discloses another type of weld tip for insertion into a weld tip plunger which includes valves within the body of the weld tip and a replaceable weld cap such that when the cap is removed the valves prevent the coolant from leaking from the weld tip. This patent does not, however, address the problem of providing coolant to multiple weld tips, any of which may be the weld tip disclosed in U.S. Pat. No. 4,788,407. It is desirable to provide a multi-tip spot welder which is able to utilize traditional hollow weld tips or weld tips having an integral valve system therein.